Flood Warnings posted as heavy rain drenches Cascades

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SEATTLE -- After taking the first half of the month off, Mother Nature has the Northwest back on her agenda as a drenching rain storm threatens to send mountain rivers over their banks this week.

However, those of you in the heart of Seattle might be scratching your heads amid some light rain and drizzle Tuesday while the rest of the region is under a deluge, thanks to the Olympic Rain Shadow.

A warm plume of moisture is moving along an atmospheric conveyor belt from the Hawaiian tropics straight into the Pacific Northwest. And snow levels around 4,000 feet Tuesday morning will rise to 6,000-7,000 feet by Tuesday afternoon. Yes, this is the dreaded Pineapple Express.

The result? A whole lot of rain in the mountains, and the potential for some flooding.

A FLOOD WARNING has been issued for the Snoqualmie, Stillaguamish, Tolt and Puyallup (near Orting) rivers. Moderate flooding is forecast on the Snoqualmie, while at this point, it's minor flooding forecast on the Tolt and Puyallup. (Flood Warnings mean flooding is occurring or imminent.)

A FLOOD WATCH remains in effect through Thursday afternoon for all other mountain-fed rivers in Western Washington. As of right now, the greatest risk of flooding is on rivers that feed out of King and Snohomish County as that is where the heaviest rain is forecast to concentrate -- some models indicate 4-7 inches of rain up there. That would include the Stillaguamish, Skykomish, and Snohomish. Other rivers with at least part of their drainage in King and Snohomish Counties include the Skagit and Cedar rivers.

But while a driving, heavy rain will be falling in the mountains, the immediate Seattle area might not see much rain at all -- like perhaps just on the order of a quarter inch or less. Models indicate such a strong upper flow that will almost be due west that a stark rain shadow is forecast to form right over Seattle and Bremerton proper -- maybe even some limited sunbreaks. (Sorry Sequim. Our turn to borrow it for a while.) So if you live in the flood plain but work in Seattle, don't be fooled into thinking the rain storm has or is missing your home. There will be a wide gradient of rain Tuesday into Wednesday between Seattle and North Bend.

Outside the rain shadow in that immediate Seattle-Bremerton area, it will be a soggy day for you too, even as close as Everett and Tacoma.

Speaking of gradient, we'll also have strong pressure gradients Tuesday that will make for an increasingly blustery day. Expect southwest winds gusting 25-35 mph for much of the day Tuesday. And as it is with flooding days, it'll be mild too. Highs will likely reach the low-mid 50s but I wouldn't be surprised to see some upper 50s where we get some downslope flow off the Olympics.

So to recap Tuesday: Rainy and windy in the mountains. Rainy and windy in much of the lowlands. Not-so-rainy-but-still-windy in Seattle and Bremerton. Mild highs in the 50s.

The rain plume is expected to slowly and gradually shift south through Tuesday night into Wednesday and rain will taper off from north to south during the day. Temperatures will likely be in the 50s to start the day but we'll gradually dip into the upper 40s in the afternoon. Winds will also gradually die down as well.

Thursday is our break with just mostly cloudy skies, but our next weather system is fast approaching and could bring light rain by the late afternoon or evening. That rain holds into Friday, but it's a routine rain with highs around 50.

Then, this weekend, we'll spin the weather pattern around to a much cooler one, as our air flow streams in from the Gulf of Alaska with even the potential for some lowland snow -- yes just days after temperatures will be flirting with 60 in some spots. As of right now, forecast models indicate this is a fringe event with snow levels perhaps around 500 feet or so and a potential Puget Sound Convergence Zone around Snohomish and northern King County that could lower snow levels there. But now that we're into late February and have longer days than the heart of winter, it's more difficult -- not impossible -- to get lowland snow. We'll see as the time draws closer. The super long range models continue the cold weather into next week.

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